The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
A camshaft actuates valves of an internal combustion engine. In a dual overhead camshaft configuration, the engine includes an exhaust camshaft and an intake camshaft for each bank of cylinders. Rotation of the camshafts actuates intake and exhaust valves of the engine. Timing of valve events can influence airflow, trapped residuals, and spark advance sensitivity, which may improve engine efficiency in fuel consumption and pollutant exhaustion.
An engine control system may include one or more camshaft phasing devices (camshaft phasors). A camshaft phasor may be used to create a continuously variable rotational offset between the exhaust camshaft and the intake camshaft and/or the crankshaft, which alters opening and closing time between intake and exhaust valves.
A camshaft phasor based control system typically includes a control valve and a phasor. The control valve is used to adjust passage of hydraulic fluid to the phasor based on a commanded position signal. The flow of hydraulic fluid controls movement of a vane within the phasor and thus relative positioning between camshafts and/or a crankshaft. Once the cam phasor is in the commanded position, fluid flow to both sides of the actuator are balanced, thereby locking the camshaft phasor in a fixed position. This control valve position is referred to as a control hold position.
The positioning of the control valve is achieved by varying the energy supplied to a solenoid which moves the control valve via a control duty cycle signal. Typically, a control hold duty cycle (CHDC) is based on a regression model that is calculated during development of a vehicle. The CHDC is calculated from a regression model that is developed over time via vehicle testing and post processing of test data. Once developed, the regression model is stored in a camshaft phasor control system of a vehicle and is unchanged. Due to component wear, accuracy of the regression model decreases over time.